The United Nations says 294,000 bedraggled and exhausted Rohingya refugees have arrived in Bangladesh since the militants' attacks on Myanmar security forces in neighbouring Rakhine state on August 25 sparked a major military backlash.

Tens of thousands more are believed to be on the move inside Rakhine after more than two weeks without shelter, food and water.

"The operation... is clearly disproportionate and without regard for basic principles of international law," Zeid said.